function Hello() {
  this.a = 1;
  this.b = 2;
}

// Hello的原型是Function,现在往Function上添加属性b和c
Hello.prototype.b = 3;
Hello.prototype.c = 4;

let say = new Hello();

console.log(Hello.prototype); // {b: 3, c: 4, constructor: ƒ}
console.log(say.__proto__); // {b: 3, c: 4, constructor: ƒ}
console.log(say.constructor.prototype); // {b: 3, c: 4, constructor: ƒ}
console.log(say.a); // 1
console.log(say.b); // 2
console.log(say.c); // 4
// console.log(say.d); // undefined
